The olfactory signals that an animal must use to find food, to find a mate, or to avoid danger consist of complex, variable mixtures of volatile chemicals. Little is yet known about the neural networks that underlie the processing of these complex odors. The experiments in this proposal take advantage of the relationship between the moth Manduca sexta and the innately attractive odor of Datura wrightii flowers, to investigate how the network of neurons in the primary olfactory center, the antennal lobe, processes this complex odor signal. As a model animal, this moth offers both well-established innate and learned olfactory-based behaviors and a brain that is accessible to multi-unit recording methods. Our preliminary results show that neurons in the antennal lobe respond maximally to a synthetic floral odor when the appropriate components are present in the proportions emitted by the natural flower. The firing rates of responding neurons decrease when the concentration of a component in the mixture is either raised or lowered. Thus, these neurons are luned" to the natural proportions of the components. We propose to investigate the role of the antennal lobe network, specifically the inhibitory interconnections among glomeruli, in producing the observed tuning. The results of these experiments can reveal a mechanism for the processing of complex, behaviorally significant olfactory stimuli at the first level of central processing. The presence of this mechanism may also clarify some conflicting models of odor mixture processing. Practically, a deeper understanding of odor processing in Manduca can inform our understanding of human olfaction, and the subtle ways in which disease can affect this sense. Finally, a mechanism for identifying complex odors can be used to create bio- mimetic devices to detect odors. Relevance: This project uses a simple experimental model animal with an interesting innate behavior to investigate how a neural circuit in the brain detects and identifies complex odors. The results of this work may demonstrate not only principles of the olfactory system, but general mechanisms that may play a role in other sensory systems. Knowledge of the subtle processes that give animals their sense of smell can lead to a better understanding of the olfactory symptoms of many brain diseases, as well as aid in developing "electronic noses" to detect harmful or noxious chemicals.